Question

Compound given below will produce effervescence when mixed with aqueous sodium bicarbonate solution 

• A. Option a
• B. Option b
• C. Option c
• D. Option d

Hint:

NaHCO\(_3\) test:
Carboxylic acids \( \rightarrow \) positive
Strong phenols (picric acid) \( \rightarrow \) positive
Normal phenols \( \rightarrow \) negative
Electron withdrawing groups increase acidity.

Answer 1

The Correct Option is D

Concept:
Effervescence with NaHCO\(_3\) indicates evolution of CO\(_2\) gas, which occurs only if compound is acidic enough to react with bicarbonate.
\[ \text{Acid} + \text{NaHCO}_3 \rightarrow \text{Salt} + \text{CO}_2 + \text{H}_2\text{O} \]
Only strong acids (carboxylic acids, highly acidic phenols) react.
Step 1: Analyze options
Nitro toluene: not acidic
Acetone: not acidic
Naphthol: weak phenol, does not react with NaHCO\(_3\)
Picric acid: strongly acidic phenol (three –NO\(_2\) groups)
Step 2: Reason
Nitro groups strongly withdraw electrons, increasing acidity of phenolic OH.
Thus picric acid behaves like a strong acid and reacts with NaHCO\(_3\).
Conclusion:
Effervescence observed only with picric acid.